The objective of this research work is to gain a better understanding of the molecular mechanism involved in the translation of genetic messages in a mammalian cell. The near term objectives are: (1) Studies of the mechanism of protein synthesis initiation in mammalian cells. These studies involve purification of peptide chain initiation factors from mammalian cells and studies of their roles in specific steps in peptide chain initiation. (2) Regulation of protein synthesis initiation in mammalian cells by heme-regulated inhibitor (HRI) and double-stranded RNA activated inhibitor (dsI). (3) Regulation of protein synthesis of mammalian cells by protein synthesis inhibitions such as low molecular weight RNAs (tcRNA), a protein synthesis interference factor (Fx) and Met-tRNAf deacylase.